| |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cygnus |
| Right ascension | 20h43m 24.192s[2] |
| Declination | 35° 35′ 16.08″[2] |
| Apparent magnitude (V) | 5.85 to 6.91[3] |
| Characteristics | |
| Spectral type | F7 Ib to G8 Ib[4] |
| Variable type | δ Cep[3] |
| Astrometry | |
| Radial velocity (Rv) | 8.1±0.2[5] km/s |
| Proper motion (μ) | RA: −6.673 mas/yr[2] Dec.: −5.108 mas/yr[2] |
| Parallax (π) | 0.8842 ± 0.0199 mas[2] |
| Distance | 3,690 ± 80 ly (1,130 ± 30 pc) |
| Absolute magnitude (MV) | −4.53[6] |
| Details | |
| Mass | 7.9–8.9[7] M☉ |
| Radius | 95.9±1.6[8] R☉ |
| Luminosity | 5,202[9] L☉ |
| Surface gravity (log g) | 1.601[10] cgs |
| Temperature | 5,315±80[8] K |
| Metallicity [Fe/H] | 0.10±0.08[8] dex |
| Rotational velocity (v sin i) | 8[7] km/s |
| Age | 31[6] Myr |
| Other designations | |
X Cyg, BD+35°4234, GC 28886, HD 197572, HIP 102276, HR 7932, SAO 70423[11] | |
| Database references | |
| SIMBAD | data |
X Cygni is a variable star in the northern constellationofCygnus, abbreviated X Cyg. This is a Delta Cephei variable that ranges in brightness from an apparent visual magnitude of 5.85 down to 6.91 with a period of 16.386332 days.[3] At it brightest, this star is dimly visible to the naked eye. The distance to this star is approximately 628 light years based on parallax measurements.[2] It is drifting further away with a radial velocity of 8.1 km/s.[5] This star is a likely member of the open cluster Ruprecht 173.[12]
The variable luminosity of this star was discovered by S. C. Chandler, Jr. in 1886.[13] In 1907, E. B. Frost showed that X Cyg is an F-type star with a varying radial velocity, behaving analogous to a Delta Cephei variable.[14] M. Luizet in 1912 found a cyclical pulsation period of 16.38543 days for the variation.[15] In 1919, F. C. Jordan determined that the color index of the star changed over the course of each cycle, becoming redder as the star grew fainter.[16] It came to be identified as a member of the benchmark class of stars termed Classical Cepheid variables that satisfy a simple period-luminosity relation.[17]
In 1954, R. P. Kraft found a stellar classification of F7 Ib at peak brightness,[18] matching the spectrum of an F-type supergiant star. The class of the star varies over the course of a pulsation cycle, ranging down to G8 Ib at minimum brightness.[4] R. P. Kraft in 1956 identified a doubling of certain spectral lines, which he explained as the result of a falling shell of matter from a prior pulsation cycle that is colliding with the photosphere.[19] Unlike most cepheid variables that undergo a single shock per cycle, X Cyg has been found to undergo a double shock.[20]
No orbiting companion has been identified with a period of ten years or less.[21] The star shows cirrus with tentative evidence for extended emission of infrared.[22]
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